Electrostatic motor

ABSTRACT

An electrostatic motor includes a cylindrical rotor and a stator. Electrodes are disposed on an inside cylindrical surface of the stator. Electrets and/or electrically conductive electrodes are disposed on the cylindrical rotor and a dielectric fluid fills space between the rotor and the stator to prevent discharge of the electrets. A mask is used to charge portions of an electret cylinder or other curved surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/631,263, filed Feb. 15, 2018, titled“Electrostatically Polarized, Radial Implementation Motor,” the entirecontents of which are hereby incorporated by reference herein, for allpurposes.

BACKGROUND Technical Field

The present invention relates to electrostatic motors and, moreparticularly, to electrostatic motors having cylindrical rotorsseparated from cylindrical stators by dielectric fluids and optionallyelectrets disposed on surfaces of the cylindrical rotors or stators.

Related Art

Various configurations of electrostatic motors have been used since themid-1700s. However, these motors performed very poorly and largely fellout of favor as much more powerful electromagnetic motors becameavailable. Most electric motors in use today rely on electromagneticeffects to produce torque, whereas electrostatic motors useelectrostatic forces. Early efforts at electrostatic motor design arereviewed in by Oleg Jefimenko, “Electrostatic Motors, Their History,Types, and Principles of Operation,” ISBN 978-1935023470, IntegrityResearch Institute, 2011. Notably, Jefimenko and his student Walkerexplored use of electrets for constructing electrostatic motors,building on the work of Russian physicist A. N. Gubkin, whose worksuggested the possibility of an electret-based motor. The electretmotors built by Jefimenko and Walker performed well compared to theirearly predecessors, but very poorly in comparison to conventionalelectromagnetic electric motors. Their designs were suitable asproofs-of-concept, but suffered from fundamental defects, which made thedesigns untenable for further commercial development.

Other elements of electret-based electrostatic motors were introduced byJapanese researchers Tada and Genda. However, the electretconfigurations of these motors were poorly designed. They pursuedconfigurations similar to the Gubkin configuration explored by Jefimenkoand Walker. Tada and Genda's motors were limited by the breakdownstrength of air.

Other potentially relevant prior art includes U.S. Pat. No. 3,696,258,U.S. Pat. Publ. No. 2006/0006759, U.S. Pat. Nos. 3,433,981 and8,264,121.

Beginning in the 1980s, several academic groups built MEMS-scaleelectrostatic motors that did not use electrets. None of these designscan be scaled up to be competitive with conventional electromagneticmotors, as they depend on physical effects suited only to micro-scaleconstruction, inasmuch as they would operate very inefficiently ifscaled to dimensions comparable to commercial electric motors.

Recently, Professor Daniel Ludois of the University of Wisconsin foundedC-Motive Corporation to commercialize electrostatic motors. Thecompany's electrostatic motor includes interleaved metal pegs or plates,which circulate in a dielectric fluid. See, for example, U.S. Pat. No.9,479,085, U.S. Pat. Publ. No. 2016/0344306 and U.S. Pat. Publ. No.2016/0099663.

Prior art electrostatic motors, even prior art electrostatic motors thatinclude electrets or dielectric fluids, suffer from various problems,such as high weight, low maximum rotation rate, very large volumes ofdielectric fluid and power supplies requiring very high voltages.

SUMMARY OF EMBODIMENTS

An embodiment of the present invention provides an electrostatic motor.The electrostatic motor includes a rotor, a stator and a dielectric. Therotor is rotatable about a rotation axis. The rotor defines a firstcylindrical surface. The first cylindrical surface has a longitudinalaxis, which is coincident with the rotation axis. The rotor has a firstplurality of charge members disposed circumferentially on the firstcylindrical surface. The first plurality of charge members is disposedcircumferentially on the first cylindrical surface. As discussed herein,each charge member of the first plurality of charge members may includean electret, an electrode or both an electret and an electrode.

The stator defines a second cylindrical surface. The second cylindricalsurface counterfaces the first cylindrical surface. The secondcylindrical surface is spaced apart from the first cylindrical surface.The second cylindrical surface is parallel to the first cylindricalsurface, and the second cylindrical surface registers with the firstcylindrical surface. The stator has a second plurality of charge membersdisposed circumferentially on the second cylindrical surface. The secondplurality of charge members is disposed circumferentially on the secondcylindrical surface. As with the first plurality of charge members, eachcharge member of the second plurality of charge members may include anelectret, an electrode or both an electret and an electrode.

One surface of the first and second cylindrical surfaces is an outsidecylindrical surface, and the other surface of the first and secondcylindrical surfaces is an inside cylindrical surface. That is, thestator may define an inside cylindrical surface that defines a volume,and the rotor may include a cylinder that fits within the volume definedby the stator's inside cylindrical surface. Conversely, the rotor maydefine an inside cylindrical surface that defines a volume, and thestator may include a cylinder that fits within the volume defined by therotor's inside cylindrical surface. In either case, the first and secondsurfaces define a cylindrical shell therebetween.

The cylindrical shell has a finite, non-zero thickness, i.e., the spacebetween the rotor's cylindrical surface and the stator's cylindricalsurface. The rotor's cylindrical surface does not touch the stator'scylindrical surface. The dielectric fills the cylindrical shell. Thedielectric takes the shape of a cylindrical shell.

In any embodiment, the dielectric may include a dielectric fluid.

In any embodiment, the dielectric fluid may be pressurized to greaterthan about 101 kPa absolute pressure.

In any embodiment, the electrostatic motor may include means forpressurizing the dielectric fluid to greater than about 101 kPa absolutepressure.

In any embodiment, the electrostatic motor may include a filter in fluidcommunication with the cylindrical shell and a pump configured tocirculate the dielectric fluid from the cylindrical shell, through thefilter and then back to the cylindrical shell.

In any embodiment, at least one surface of the first and secondcylindrical surfaces may define a plurality of features that extendproud of the at least one surface. In any embodiment, the each featureof the plurality of features may include a chevron shape.

In any embodiment, the dielectric may include a partial vacuum.

In any embodiment, one plurality of charge members of the first andsecond pluralities of charge members may include a plurality ofelectrets arranged such that adjacent electrets are of opposite charge,and the other plurality of charge members of the first and secondpluralities of charge members may include a first plurality ofelectrodes.

In any embodiment, charges on adjacent electrets of the plurality ofelectrets may be sufficient to exceed breakdown voltage of air over adistance equal to spacing between the adjacent electrets.

In any embodiment, the one plurality of charge members further comprisesa second plurality of electrodes.

In any embodiment, the electrostatic motor may also include a pluralityof charging electrodes, one charging electrode of the plurality ofcharging electrodes for each respective electret of the plurality ofelectrets. Each charging electrode may be disposed below, i.e., awayfrom the cylindrical surface, and in intimate contact with, therespective electret.

In any embodiment, the one plurality of charge members of the first andsecond pluralities of charge members may include a first plurality ofelectrodes, and the other plurality of charge members of the first andsecond pluralities of charge members may include a second plurality ofelectrodes.

In any embodiment, the electrostatic motor may also include anelectronic circuit configured to energize and commutate one plurality ofcharge members of the first and second pluralities of charge members.

In any embodiment, the rotor may define a plurality of first cylindricalsurfaces. Each first cylindrical surface may have a respectivelongitudinal axis coincident with the rotation axis. Each firstcylindrical surface may have a first plurality of charge membersdisposed circumferentially thereon. The stator may define a plurality ofsecond cylindrical surfaces. Each second cylindrical surface maycounterface, and be spaced apart from, a corresponding one of the firstcylindrical surfaces. Each second cylindrical surface may have a secondplurality of charge members disposed circumferentially thereon.

In any embodiment, the electrostatic motor may include a hydrostaticbearing. The hydrostatic bearing may be configured to support the rotorwithin the stator. The hydrostatic bearing may define a plurality offluid ports. Each fluid port extends from an outer surface of the statorto an inner surface of the stator. At least some of the fluid portsextend through the second plurality of charge members. One end of eachfluid port may be in fluid communication with the cylindrical shell.

Another embodiment of the present invention provides a rotor for anelectrostatic motor. The rotor includes a cylinder. The cylinder isrotatable about a rotation axis. The cylinder defines a firstcylindrical surface. The first cylindrical surface has a longitudinalaxis that is coincident with the rotation axis. The rotor has aplurality of electrets disposed circumferentially on the firstcylindrical surface.

The rotor also has a plurality of charging electrodes, one chargingelectrode of the plurality of charging electrodes for each respectiveelectret of the plurality of electrets. Each charging electrode beingdisposed below, i.e., away from the cylindrical surface, and in intimatecontact with, its respective electret. The plurality of chargingelectrodes is electrically accessible via at least one electricallyconductive port through a surface of the rotor. The port may be at thesame level as the cylindrical surface, or the port may be located in adepression in the cylindrical surface. The port may be located on aboss. The port may be located elsewhere on the rotor.

Yet another embodiment of the present invention provides a method ofmanufacturing a rotor for an electrostatic motor. The method includesforming a plurality of electrets, such that the plurality of electretsis disposed circumferentially on a cylindrical surface of the rotor. Themethod also includes preventing formation of an air path betweenadjacent electrets of the plurality of electrets.

In any embodiment, preventing formation of the air path may includeapplying a dielectric fluid to the cylindrical surface.

In any embodiment, preventing formation of the air path may includeforming a partial vacuum around the cylindrical surface.

An embodiment of the present invention provides a fixture for contactcharging a cylindrical electret workpiece having a longitudinal axis.The fixture includes a first plurality of spaced-apart electrodes. Thefirst plurality of spaced-apart electrodes is arranged along animaginary cylindrical surface having a longitudinal axis coincident withthe longitudinal axis of the workpiece. All electrodes of the firstplurality of spaced-apart electrodes are electrically connected togetherto form a first circuit. The fixture also includes a second plurality ofspaced-apart electrodes arranged along the imaginary cylindricalsurface. All electrodes of the second plurality of spaced-apartelectrodes are electrically connected together to form a second circuit.The second circuit is electrically isolated from the first circuit. Eachelectrode of the second plurality of spaced-apart electrodes is disposedbetween two adjacent electrodes of the first plurality of spaced-apartelectrodes.

In any embodiment, the fixture may also include an electricallyinsulated cylinder disposed around, and in intimate contact with, eitheran outer surface or an inner surface of the first and second pluralitiesof spaced-apart electrodes. A longitudinal axis of the electricallyinsulated cylinder is coincident with the longitudinal axis of theworkpiece.

In any embodiment, the fixture may include means for changing diameterof the electrically insulated cylinder, thereby changing diameter of theimaginary cylindrical surface.

In any embodiment, the fixture may include a screw configured to changethe diameter of the electrically insulated cylinder, thereby changingthe diameter of the imaginary cylindrical surface.

Yet another embodiment of the present invention provides a fixture forcontact charging a cylindrical electret workpiece having a longitudinalaxis. The fixture includes an electrode assembly that includes a firstelongated electrode, a second elongated electrode and an electricallyinsulated material between the first and the second electrode. The firstelectrode is electrically isolated from the second electrode. Alongitudinal axis of the first electrode is parallel to a longitudinalaxis of the second electrode and parallel to the longitudinal axis ofthe workpiece. The electrode assembly is translatable, between a firstposition and a second position, along an axis perpendicular to thelongitudinal axis of the workpiece. The electrode assembly is configuredsuch that, in the first position, the first and second electrodes are inintimate physical contact with a cylindrical surface of the workpiece.The electrode assembly is configured such that, in the second position,the first and second electrodes are spaced apart from the surface of theworkpiece.

In any embodiment, the electrode assembly may be configured such thatthe cylindrical surface of the workpiece is an outside cylindricalsurface of the workpiece.

In any embodiment, the electrode assembly may be configured such thatthe cylindrical surface of the workpiece is an inside cylindricalsurface of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood by referring to thefollowing Detailed Description of Specific Embodiments in conjunctionwith the Drawings, of which:

FIG. 1 is an isometric diagram, and

FIG. 2 is a perspective cut-away diagram, of an assembled electrostaticmotor, according to an embodiment of the present invention.

FIG. 3 is an exploded isometric view of the electrostatic motor of FIGS.1-2.

FIG. 4 is an exploded isometric view of a rotor assembly of theelectrostatic motor of FIGS. 1-2.

FIG. 5 is an end view, and

FIG. 6 is a cross-sectional view of the electrostatic motor of FIGS.1-3.

FIG. 7 is an enlarged view of a portion of FIG. 6.

FIG. 8 is a side view, and

FIG. 9 is a cross-sectional view of the electrostatic motor of FIGS.1-3.

FIG. 10 is a cross-sectional view of the electrostatic motor of FIGS.1-3, similar to FIG. 9, but with additional detail, and

FIG. 11 is an enlarged view of a portion of FIG. 10, showing forcesgenerated within the motor.

FIG. 12 is an enlarged view of a portion of FIG. 9 showing motorcomponents, and

FIG. 13 is the enlarged view of the portion of FIG. 9 showing forces andresulting rotation of the rotor.

FIG. 14 is an enlarged view of a portion of FIG. 9 showing regions ofconductive material within the rotor that form embedded chargingelectrodes, according to an embodiment of the present invention.

FIG. 15 is an isometric view,

FIG. 16 is a side view,

FIG. 17 is a cross-sectional view and

FIG. 18 is an enlarged view of a portion of the rotor with an optionalcoating of an electrically conductive material, according to anembodiment of the present invention.

FIG. 19 is an isometric diagram illustrating a contact charging fixture,according to an embodiment of the present invention.

FIG. 20 is an isometric diagram of the contact charging fixture of FIG.19, with an outer cylinder removed for clarity.

FIG. 21 is a side view of the contact charging fixture of FIG. 19.

FIG. 22 is a cross-sectional view through the contact charging fixtureof FIG. 21, and

FIG. 23 is an enlarged view of a portion of FIG. 22.

FIG. 24 is an isometric diagram of a mask with an aperture, throughwhich ions may be guided to corona-charge a defined region in anelectret cylinder or other curved surface, according to an embodiment ofthe present invention.

FIG. 25 is an isometric schematic diagram of an apparatus, including themask of FIG. 24, of a corona charging system, according to an embodimentof the present invention.

FIGS. 26, 27 and 28 are respective exploded, cut-away exploded andcut-away assembled perspective view diagrams of an electrostatic motorthat includes multiple concentric cylindrical rotors and stators,according to an alternate embodiment of the present invention.

FIG. 29 is an isometric diagram illustrating a contact charging fixture,spaced apart from a dielectric cylinder, according to another embodimentof the present invention.

FIG. 30 is an isometric diagram illustrating the contact chargingfixture of FIG. 29 in contact with the dielectric cylinder, according tothe embodiment of the present invention.

FIG. 31 is an isometric diagram of a hydrostatic or aerostatic bearingbetween a rotor and a stator of an electrostatic motor, according to anembodiment of the present invention.

FIG. 32 is a cross-sectional view of a portion of the rotor and statorshown in FIG. 31, showing one fluid port of the hydrostatic oraerostatic bearing, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Definitions

As used herein, including in the claims, unless otherwise indicated incontext, the following terms shall have the following meanings.

A cylinder (or circular cylinder) is a curvilinear surface, notnecessarily a solid. A cylinder is the locus of points traced by afinite-length line segment rotated about an axis, where the line segmentis co-planar with the axis, but the line segment is not perpendicular tothe axis. The line segment may be straight, curved or formed of aplurality of straight and/or curved sub-segments. If the line segment isparallel to the axis, the cylinder is a conventional right cylinder. If,however, the line segment is not parallel to the axis, the cylinder maybe tapered, i.e., shaped like a cone or a portion of a cone.

A circular hollow cylinder (or cylindrical shell) is a three-dimensionalregion bounded by two circular cylinders having the same axis, twoparallel sides and two parallel (not necessarily equal diameter) annularbases perpendicular to the cylinders' common axis.

Commutation is a process of switching electric current and/or voltage inmotor phases to generate motion. Brushed motors have physical brushes toachieve this process twice or more per rotation, while brushless directcurrent (BLDC) electric motors do not. Due to the nature of theirdesign, BLDC motors can have any number of pole pairs for commutation.Similarly, electrostatic motors can have any number of electrodes forcommutation.

An electrode is an electrical conductor through which electric currentand/or charge enters or leaves an object, substance or region.

An electret is a material that retains a permanent or semi-permanentelectric charge after exposure to a strong electric field.

A dielectric (or dielectric material) is an electrical insulator thatcan be polarized by an applied electric field.

An electrical conductor is a material having an electrical resistivityless than about 10⁻⁶ Ω-m.

An electrical insulator is a material having an electrical resistivitygreater than about 10⁻⁶ Ω-m.

A partial vacuum is a region with a gaseous pressure less than about 40Pa. A partial vacuum is a dielectric.

A fluid is any liquid, gas, supercritical fluid or multiphase mixture ofliquid, gas and/or supercritical fluid that has a suitably highdielectric breakdown strength, permittivity and/or low viscosity.

Cylindrical Electrostatic Motor

Embodiments of the present invention provide electrostatic motors thatimprove upon the efficiency, weight and cost of conventionalelectromagnetic electric motors and electric motor-driven systems. Theseembodiments operate more efficiently over a wider range of speeds thanconventional electric motors and known electrostatic motors, weigh lessand cost less. By operating more efficiently than conventional motors,machines powered by these embodiments are less costly to operate,because they consume less power. The improved efficiency of theseembodiments, in combination with their low weight, enable vehicles totravel further and/or bear a larger payload, since a lower volume andmass of batteries, or other energy storage devices, is required. Thelower cost and weight of these embodiments is due to the replacement ofexpensive and heavy materials used in conventional electromagneticmotors, such as magnets, copper wire and electrical steels, withinexpensive, lightweight electret materials and/or thin, conductiveelectrodes.

These motors can be used to power a wide range of machines that now relyon electromagnetic electric motors. The list of potential applicationsincludes, but is not limited to: vehicles (including primary drivetrainand auxiliary motors for motor vehicles, drones, etc.), aircraft,watercraft (including boats and underwater vehicles), electric tools,robots, manufacturing/material handling equipment, constructionequipment, HVAC (heating, ventilation, and air conditioning) equipment,toys and medical devices. The motors are also capable of operating asgenerators, so they have applications in electricity generation, energyscavenging and hybrid motor/generators.

FIG. 1 is an isometric diagram, and FIG. 2 is a perspective cut-awaydiagram, of an assembled electrostatic motor 100, according to anembodiment of the present invention. FIG. 1 shows a case 102, front endcap 104 of the case 102, shaft 106 and axis 108. FIG. 2 shows acylindrical rotor 202 with a plurality of alternatingly chargedelectrets, represented by electrets 204 and 206, disposed on an outsidesurface of the rotor 202. The rotor 202 rotates about the axis 108. Aplurality of electrodes, represented by electrodes 208, 210, 212 and214, is disposed on an inside cylindrical surface of a dielectricsubstrate 215 to form a stator 216. Ones of the electrets 204-206 of therotor 202 register with, counterface, are coaxial with, and spaced apartfrom, the electrodes 208-214 of the stator 216 to define a cylindricalshell between the electrets 204-206 and the electrodes 208-214, althoughthe number of electrets 204-206 need not equal the number of electrodes208-214. In some embodiments, the cylindrical shell may be on the orderof 100s of μm thick. In other embodiments, the cylindrical shell may bethicker or thinner than 100s of μm thick. A dielectric fluid (not shownin FIG. 2), or a partial vacuum, fills the cylindrical shell.

Force generated by any electric motor is defined by the well-knownLorentz force equation (1):F=qν×B+qE  (1)In magnetic motors, the value of the term qν depends on an electriccurrent in a coil of wire, and the value of the term B depends on thestrength of a magnetic field from a permanent magnet or anelectromagnet. In an electrostatic motor, the value of the term qEdepends on the strengths of a static charge (q) and an electric field(E).

FIG. 3 is an exploded isometric view of the electrostatic motor 100.FIG. 3 shows the case 102, front end cap 104 and shaft 106, front andrear bearings 300 and 302, respectively, rear end cap 304, thedielectric substrate 215 on which are formed or disposed driveelectrodes 306 (corresponding to electrodes 210-224 in FIG. 2), such asin slots 308, and a rotor assembly 310. Collectively, the dielectricsubstrate 215 and the electrodes 306 form the stator 216.

FIG. 4 is an exploded isometric view of the rotor assembly 310,including the shaft 106, an electret cylinder 400, which includesalternatingly polarized electrets 402 (or alternatively electricallyconductive bands, or alternatively both electrets and electricallyconductive bands), and front and rear end caps 404 and 406,respectively.

FIG. 5 is an end view, and FIG. 6 is a cross-sectional view, of theelectrostatic motor 100. FIG. 7 is an enlarged view of a portion of FIG.6, as indicated by an arrow 600. Much of the motor 100 can be empty, asindicated at 602, thereby reducing its weight, compared to conventionalelectromagnetic motors. A cylindrical shell 700 is defined between theelectrets 402 and the drive electrodes 306.

FIG. 8 is a side view, and FIG. 9 is a cross-sectional view, of theelectrostatic motor 100. A portion 900 of FIG. 9 is shown enlarged inFIGS. 12 and 13. FIG. 10 is a cross-sectional view of the electrostaticmotor 100, similar to FIG. 9, but with additional detail. FIG. 10illustrates a rotor 1000 and a stator 1002 with a dielectric fluid 1004therebetween. FIG. 11 is an enlarged view of a portion 1006 of FIG. 10,showing forces, exemplified by repulsion and attraction forces 1100 and1102, respectively, generated within the motor 100. Dimensions of theelectrets and electrodes are exaggerated for clarity.

FIG. 12 is an enlarged view of a portion of FIG. 9 showing motorcomponents, and FIG. 13 is the enlarged view of the portion of FIG. 9showing forces and resulting rotation of the rotor assembly 310. In FIG.13, attractive and repelling forces between drive electrodes andelectrets (or rotor electrodes) are indicated at 1300 and a direction ofnet rotation of the motor 100, caused by torque resulting from theforces 1300, is indicated by an arrow 1302.

Rotor with Electrodes Embedded in Bulk Electret Material to FacilitateCharging

In some embodiments, the rotor includes electrically conductive materialembedded in the bulk electret material to form embedded chargingelectrodes. These electrodes facilitate contact charging, without needfor external charging fixtures, thus simplifying the process formanufacturing an electret rotor. Furthermore, the rotor surface can besubmerged in dielectric fluid during charging, which prevents airbreakdown near the rotor surface or accumulation of charged particles onthe rotor, providing further advantages. FIG. 14 is an enlarged view ofa portion 900 of FIG. 9, which shows a cross-section through the motor,showing regions of conductive material within the rotor that formembedded charging electrodes 1400. Optionally, additional regions ofelectrically conductive material (not shown) may be disposed on theouter surface of the rotor, radially registered with, but radiallyspaced apart from, the embedded charging electrodes 1400. Embodimentswith both outer and embedded charging electrodes provide choices forcharging the electrets. Charging the electrets can be performed byapplying a voltage across circumferentially adjacent charging electrodeson the outside of a rotor, across circumferentially adjacent chargingelectrodes on the inside of a rotor and across radially adjacentcharging electrodes, i.e., one charging electrode on the outside of therotor and one charging electrode on the inside of the rotor. Chargingthe electrets according to these choices yields different chargepatterns and charge densities.

To embed electrodes within a bulk electret material, a layer ofconductive material may be deposited on the surface of a cylinder ofelectret material using known methods, such as sputtering or chemicalvapor deposition (CVD). The conductive material is patterned, such asthrough shadow masking, to form discrete electrodes. Next, a layer ofelectret material is deposited on top of the electrodes deposited in theprevious step, burying most of the conductive material. The electretmaterial may be deposited by over-molding, chemical vapor deposition orany other suitable method. The final layer of electret material isprevented from covering a small region of each embedded electrode, suchas by masking or other suitable method, such that portions of theembedded electrodes remain physically accessible for connection to avoltage source.

The electret material is then polarized by connecting adjacent, embeddedelectrodes to positive and negative poles of a voltage source,respectively, which thereby creates an electric field within theelectret material between the adjacent embedded electrodes, causing thatportion of material to become polarized.

In some embodiments, charging electrodes 1400 of every other electretare electrically connected together within the rotor, forming twocircuits, one circuit for electrets that are to be positively charged,and the other circuit for electrets that are to be negatively charged.Nevertheless, each electret is considered to have a respective chargingelectrode 1400.

In the embodiment shown in FIGS. 1-13, electrets are disposed on thesurface of the rotor assembly 310, and electrodes 306 (208-214) aredisposed on the inside surface of the stator 216. However, in some otherembodiments, the electrets are disposed on the inside surface of thestator 216, instead of or in addition to the electrodes 306 (208-214),and other electrodes are disposed on the surface of the rotor assembly310. In these embodiments, electrical signals are sent to the rotorassembly 310, rather than the stator 216, such as via brushes or sliprings, to commutate the motor 100.

In the embodiment shown in FIGS. 1-13, the rotor assembly 310 isdisposed within the stator 216, and the rotor assembly 310 is a cylinderwith an outside surface that counterfaces an inside cylindrical surfaceof the stator 216. The rotor assembly 310 spins within the stator 216.However, in some other embodiments, the rotor assembly 310 spins outsidethe stator 216. In these other embodiments, the stator is configured asa cylinder with electrodes and/or electrets on its outside surface, andthe rotor defines an inside cylindrical surface that counterfaces thestator.

In general, electrostatic motors generate torque by electrostaticattraction or repulsion between charged surfaces. Motors, according toembodiments of the present invention, include a cylindrical rotor 202(FIG. 2) with an outer surface made of a plurality of polarized electretmaterials and/or conductive electrodes, represented by electrets204-206. The motors also include a case 102 with a cylindricalarrangement of conductive electrodes, represented by electrodes 208-214that surround the rotor 202. The electrodes 208-214 collectively form astator 216. A thin cylindrical shell of dielectric fluid (not shown inFIG. 2), but shown at 1004 in FIGS. 10 and 11, is situated between theouter surface of the rotor 202 and the stator 216. In some embodiments,as little as a few milliliters of dielectric fluid fill the spacebetween the outer surface of the rotor 202 and the stator 216.

Some embodiments use electret rotors. In these embodiments, electrets204-206 (402) and drive electrodes 208-214 (306) are arranged such thatby applying positive and negative voltages to the drive electrodes 306,electrically charged regions 402 on the rotor 102 are electrostaticallyattracted to, or repelled from, nearby electrodes 306, causing a nettorque to be applied to the rotor, causing it to rotate, asschematically illustrated in FIG. 11. The electrodes 208-214 (306) aremanufactured onto a substrate material, such as alumina, with a highdielectric constant to prevent discharges (arcing) between theelectrodes. By varying the polarities of voltages on the driveelectrodes 208-214 (306) over time, a sustained clockwise orcounterclockwise torque is applied to the rotor 1002, causing continuousrotation of the shaft. The magnitude of the torque depends on theintensities of the electric fields that the electrodes 208-214 (306)apply to the rotor 1002, charge on the electrets 204-206 (402), numberof counterfacing electrode/electret pairs (although there need notnecessarily be equal numbers of electrets on the rotor as electrodes onthe stator) and radius at which the electrets are disposed from thecenter of the shaft. Optionally, each electrode 208-214 (306) issurrounded by an electrically, floating-potential conductive guard ringor field plate, exemplified by ring 1106, to shape the electric field ofthe electrode 306, as is known in the art.

The angle subtended by each electrode (equivalently, the circumferentialwidth of each electrode) can be made very small, on the order of 1 μm.Thus, the stator may have a very large number of drive electrodes. Thenumber of drive electrodes can thus greatly exceed the number ofpolarized regions of electret material, thus a very large number ofphases may be independently activated to reduce torque ripple andimprove motor efficiency.

An external power supply (not shown) applies voltages to the driveelectrodes, and a switching circuit (not shown) modulates the voltages,i.e., commutates the motor, depending on the real-time angular positionof the rotor, such that a net torque is consistently applied in adesired orientation. The power supply and switching circuit energize theelectrodes to commutate the motor in a manner analogous to aconventional brushless direct current motor. The angular position of therotor may be sensed using an electrostatic method described herein, orby conventional angular position sensors, such as optical encoders, Halleffect sensors or the like. The switching circuit may includesemiconductor devices, such as field-effect transistors, bipolartransistors, commutator brushes and other related components capable ofswitching high voltages, as is well known in the art.

In an alternate embodiment, the electrets are either replaced orsupplemented with conductive electrodes (“rotor electrodes”), and therotor electrodes are charged by an external voltage source.

Dielectric Fluid Between Rotor and Stator

In general, large electric fields are not stable, because air becomesconductive, i.e., ionizes (breaks down), in an electric field exceedingapproximately 3 MV/m. The dielectric fluid 1004 (FIG. 10) in some motorembodiments enables very high electric fields to be applied to the rotorfrom the electrodes without breakdown, enabling much higher torque thanwould be possible with an air gap between the electrodes and theelectrets/rotor electrodes. A low viscosity dielectric fluid ispreferred, such as an alkane hydrocarbon fluid or fluorocarbon fluid,since low viscosity enables high shaft rotation speeds with low fluidfrictional losses. However, a high viscosity dielectric fluid may besuitable where relatively low shaft speed is acceptable, such as in arobot arm.

Suitable dielectric fluids may include alkanes, perfluorocarbons,purified water, silicone oil, mineral oil and other chemicals known inthe art. Suitable nanoparticles may be added to the dielectric fluid toincrease electrical breakdown strength.

In an alternate embodiment, the dielectric fluid is a high partialvacuum established within the motor case, such as by a vacuum pump. Avacuum-compatible rotary seal, such as a ferrofluidic seal or end-facemechanical seal, as known in the art, enables the rotating motor shaftto penetrate the case without loss of vacuum. A high partial vacuum canreplace the dielectric fluid because it has a very high electric fieldbreakdown strength. In some embodiments, the partial vacuum has apressure below about 1 mTorr (0.13 Pa). Specific vacuum requirementsdepend on electrode (or electret) spacing and drive voltage and may becalculated by reference to Paschen's law. Such a partial vacuum providesan efficiency advantage because fluid friction energy losses that wouldresult from dielectric fluid are eliminated.

In a related embodiment, a dielectric fluid is installed in thecylindrical shell between the rotor and case, but air in the remainderof the empty space within the case is replaced by a partial vacuum or aninert gas, such as nitrogen. Replacement of the air is advantageous formaintaining purity of the dielectric fluid, which may otherwise becomecontaminated by atmospheric gases within the air.

Multiple Concentric Cylindrical Arrangement

In another alternate embodiment, multiple concentric cylindricalarrangements, exemplified by cylinders 2700 and 2702, of polarizedelectret material are attached to one or more discs, such as disc 2704,that are attached to the shaft 106, as shown in FIGS. 26-28. One or moreother discs, exemplified by disc 2706, are attached to the case andsupport electrodes that are disposed in multiple concentric cylindricalarrangements, exemplified by cylinders 2708, 2710 and 2712. Theelectrodes extend from these discs 2708-2712 to apply electric fields tothe multiple electret cylinders 2700-2702. It should be noted thatelectrodes and electrets may be disposed on one or both surfaces of eachcylinder 2708-2712 and 2700-2702, for example as shown at 2714 and 2716.This configuration provides more torque than with a single electretcylinder and is suited to applications where a large diameter isavailable for a motor, but length of the motor is limited. Thedisadvantage of this approach is that the weight of the motor isincreased.

FIG. 15 is an isometric view, FIG. 16 is a side view, and FIG. 17 is across-sectional view of the electret cylinder 400 of the rotor assembly310. FIG. 18 is an enlarged view of a portion 1700 of the electretcylinder 400. As shown in FIG. 18, in another embodiment, the electretrotor is coated in a thin layer of electrically conductive material1800, which concentrates electret charge near the surface of the rotorand also concentrates the electric field emanating from electrode pairsat the surface of the rotor. By concentrating both the electric fieldfrom the electrodes and the charge from the electrets close to the rotorsurface, a higher torque can be applied to the rotor than if theconductive coating is absent.

Furthermore, the electrically conductive material 1800 prevents directphysical contact between the dielectric fluid 1004 and the electrets402. Such contact can cause an accumulation of charge that damages theelectrets 402. In some embodiments, the layer of electrically conductivematerial 1800 is segmented by electrically insulative material,exemplified by electrical insulators 1802. Optionally, the electricallyconductive material 1800, or ones of the segments of electricallyconductive material, is connected to a voltage supply to rechargedepleted electrets.

Dielectric Fluid Filtration

Performance of the dielectric fluid may degrade over time byinfiltration of particles, bubbles and/or dissolved atmospheric gases.To exclude these contaminants, a rotary seal may be installed at theend(s) of the case, where the shaft protrudes. Suitable rotary sealsinclude ferrofluidic seals and end-face mechanical seals.

Another method for avoiding performance loss due to particle, bubblesand/or dissolved gases is to enable the dielectric fluid to bereplenished from a reservoir of purified dielectric fluid. Thedielectric fluid reservoir may be pressurized with an atmosphere ofinert gas, such as nitrogen, and routed to the interior of the motor.When it becomes necessary to replace the fluid, a mechanical orelectronically actuated valve may be opened to drain the contaminateddielectric fluid, and to allow the fluid stored in the reservoir todisplace the contaminated fluid. The reservoir is preferably adetachable cartridge, which can be replaced as necessary to maintainoptimal dielectric fluid quality.

In another embodiment, a large pressure is externally applied to thedielectric fluid. When pressurized, the dielectric fluid can support alarger electric field without breakdown than when no pressure isapplied. This beneficial effect increases approximately linearly withincreased pressure above atmospheric pressure. The pressure may begenerated mechanically, such as with a compressed spring that appliesforce to a piston situated in fluid communication with the dielectricfluid, or with a pressurized, inert gas, such as nitrogen, that appliespressure to a surface of the dielectric fluid. An additional benefit ofthis configuration is that the pressurized fluid acts as a hydrostaticbearing, which helps stabilize and lower friction on the rotor, andmaintain a very small gap between the rotor and the stator. Oneadvantage of the small gap between the rotor and the stator is that themotor can produce a large torque, relative to other configurations thatwould require a larger gap. Another advantage of the small gap is thatthe motor can be operated with lower voltages than would be required ifthe gap were larger. In a related embodiment, the surface of the rotoris patterned with three-dimensional features, such as chevron shapesexemplified by chevron 1500 in FIG. 15, that locally increase thepressure of the dielectric fluid when the rotor is in motion, asindicated by an arrow 1502, boosting the fluid's breakdown strength.

Accumulation of charged particles on the surfaces of electrets maycancel the electret charges and degrade performance of the motor. Someembodiments include a charging and cleaning mode, in which asufficiently large voltage is applied between each adjacent pair ofelectrodes. The large voltage creates a strong electric field gradient,which displaces entrapped particles from the surfaces of the electretswhile also polarizing the electrets to a desired level of charge.

Some embodiments include components to continuously, periodically oroccasionally clean the contaminated dielectric fluid of particles,bubbles and/or dissolved gases. In some such embodiments, impellersextending from the rotor cause the dielectric fluid to be pumped througha filter, such as a porous membrane or an electrostatic or magneticfilter. An advantage of an electrostatic filter is that the motor'selectric power supply may be sufficient to power the electrostaticfilter. In both of the above embodiments, the impellers, which form aninternal pump, may be replaced by a conventional, secondary pump, suchas a peristaltic pump, scroll pump or other suitable fluid pump.

Real-Time Angular Measurement of Rotor/Shaft

Some embodiments detect real-time angular position of the rotor assembly310, without a need for additional sensors, such as optical encoders,magnetic sensors, resolvers or the like. It is useful to detect therotor position, for accurate rotor positioning and speed control, anddoing so without additional sensors simplifies the motor and reduces itscost, size and weights. In these embodiments, to measure the shaft 106angle, the rotor is extended such that a small portion of each chargedelectret band, or rotor electrode, extends past the ends of the driveelectrodes. A secondary arrangement of two or more sensing electrodes isattached to the interior of the case, near the extended portion of therotor, and is electrically isolated from the electrodes that are used toapply torque to the rotor. As the rotor spins, the motion of theelectrets causes electrical charges to be induced on the sensingelectrodes. The physics of electrostatic induction causes the magnitudesof these charges to vary in relation to the angle of the shaft, and thecharges can be measured using standard voltage measurement circuits, asare known in the art. The angular position of the shaft can be inferredby the magnitude of these measured voltages.

Geometry of Cylindrical Electrostatic Motor

Embodiments of the present invention include a particular geometricarrangement of electrets 402, or rotor electrodes, and drive electrodes306 that is distinct from previous motors. In particular, disposing theelectrets 402 and/or electrodes on a cylindrical surface, rather than ona surface of a disk or on pegs, provides advantages. For example, allthe electrets 402 and/or electrodes are disposed a radial distance (forexample, the radius of the rotor's electret cylinder 400) from the shaft106. Therefore, electrostatic forces 1300 acting on these electrets 402and/or electrodes act through a moment arm equal to the radius to applytorque to the shaft 106. In disc-based electrostatic motors, chargesacting on portions of the disc close to the shaft apply far less torquethan charges acting on portions of the disc close to the circumferenceof the disc. Furthermore, electret rotor embodiments combine twoelements that have not previously been combined in a rotary motor: (1)electrets 402 and (2) dielectric fluid 1004.

Both surfaces in contact with the dielectric fluid 1004, i.e., thesurface of the rotor 1000 and the surface of the stator 1002, aresmooth, relative to conventional electric motors, thus these smoothsurfaces create much less fluid drag than conventional motors, leadingto improved efficiency of the electrostatic motor. The volume ofdielectric fluid 1004 used to fill the gap 700 between the rotor andstator is very small, relative to other motors (such as the motordescribed in U.S. Pat. Publ. No. 2016/0344306) that use dielectricfluid, owing to the small distance between the rotor 1000 and the stator1002. Thus, the fluid weight is also small, the cost of the fluid is lowcompared to motors that require a larger volume of fluid, and the fluidis easier to dispose of.

The embodiments described herein were arrived at with the aid ofadvanced computer modeling tools, such as finite element analysis, whichwere not available to earlier generations of electrostatic motordesigners, and required multiple design iterations and experimentationwith geometry and material properties. Furthermore, the electret rotorembodiments were inspired in part by our knowledge and experience withstate-of-the-art electret materials and manufacturing methods, whichwere not known to earlier designers, such as Jefimenko and Walker, andalso our analysis of state-of-the-art, high-breakdown dielectric fluids.

Several textbooks have “taught away” from pursuing electrostatic motorsat scales larger than the micro-scale, arguing that the breakdownstrength of air presents a fundamental limitation, discouraging inquiryinto the subject.

Methods and Apparatus for Charging Defined Regions on a CylindricalElectret

Another aspect of the present invention involves apparatus and methodsfor contact charging defined regions on a cylindrical electret.Conventional contact charging is a well-known method for polarizing flatelectrets. However, conventional contact charging methods are inadequatefor charging defined regions on a cylindrical electret. FIG. 19illustrates a contact charging fixture 1900 that may be used to polarizea cylinder of electret material 400 with multiple, positively chargedregions and multiple negatively charged regions. The cylinder ofelectret material 400 is inserted into a bore 1902 of the contactcharging fixture 1900, by advancing the cylinder 400 in a directionshown by an arrow 1904. The contact charging fixture 1900 includes anarrangement of electrically conductive electrodes, exemplified byelectrodes 1906, 1908 and 1910, attached to a non-conducting cylinder1912. The non-conducting cylinder 1912 maintains physical separationbetween positively charged and negatively charged portions of theconductive electrodes 1906-1910, thus preventing electrical shortingbetween them.

FIG. 20 is a view of the contact charging fixture 1900, with thenon-conductive cylinder 1912 removed for clarity. The number of chargingelectrodes, here exemplified by charging electrode 2000, is equal to thenumber of regions on the electret cylinder 400 that will becomepolarized during contact charging. A first electrically conductive ring2002 at one end of the charging fixture is an electrically common pointfor one group of charging electrodes. A second electrically conductivering 2004 at the opposite end of the charging fixture is an electricallycommon point for a second group of charging electrodes, to be chargedwith opposite polarity to those charged with electrodes common to thefirst conductive ring 2002. To charge the electret cylinder, one polefrom an electrical power supply (not shown) is connected to the firstring 2002, and the opposite pole is connected to the second ring 2004.Electric fields are thus created within the electret cylinder betweenpositive and negative charging electrodes 2000, causing electretmaterial within the electric fields to be polarized.

It is advantageous to apply pressure from electrodes to electrets duringcontact charging. The contact charging fixture 1900 may apply pressureto the electret cylinder, for example by selectively constricting thefixture around the electret cylinder or by expanding the fixture beforeinsertion of the electret cylinder and then, after insertion of theelectret cylinder, elastically contracting around the electret cylinder.The charging fixture's diameter may be made compliant by removingportions of material 2006 from one or both end rings 2002 and 2004. InFIG. 20, the end rings 2002 and 2004 are shown to be completely severedto define gaps 2006 and 2008 in the end rings. Compliance may be also beincreased without severing the rings, such as by selectively removingmaterial, as is commonly done to create flexural springs usingwell-known methods. To constrict the charging fixture about an electretcylinder, the end ring diameters may, for example, be reduced bywrapping a tensionable strap around either end ring or both end rings oraround the structure shown in FIG. 20 or around the non-conductivecylinder 1912, or by bridging a gaps 2006 and 2008 with respectivescrews (not shown), such that rotation of the screws draws opposingfaces of the gaps together.

FIG. 21 is a side view of the contact charging fixture 1900 with anelectret cylinder 400 (not visible) inserted therein. FIG. 22 is across-sectional view through both the contact charging fixture 1900 andthe electret cylinder 400. FIG. 23 is an enlarged view of a portion 2200of FIG. 22. A charging electrode 2000 is shown in a chargingconfiguration, with an inner, curved surface interface 2300 of thecharging electrode 2000 in intimate contact with a region that willbecome an electret 402 (once polarized) on the electret cylinder 400.The curved surface 2300 may be coated with a conductive liquid, such asmercury, or another conductive material, such as gallium or a eutecticalloy, preferably with a lower melting point than the charging electrodeto promote transfer of charges to the electret by liquid charging.Liquid-contact charging is a method known to those with ordinary skillin the art for charging of flat electrodes.

Although the contact charging FIG. 1900 has been described for use increating electrets on the outside surface of a cylindrical surface, thecontact charging FIG. 1900 can, with suitable modifications, be used tocreate electrets on the inside surface of a cylindrical surface. In thiscase, the non-conductive surface 1912 may be placed on the inside of theelectrodes 1906-1910, rather than on the outside, and electrodes1906-1910 may be placed inside the cylinder to be processed. After thefixture 1900 is inserted into the cylinder, the fixture 1900 may beexpanded to apply pressure on the inside of the cylinder. Alternatively,the fixture 1900 may be constricted before being inserted into thecylinder, and then allowed to expand once inside the cylinder to applythe pressure to the inside of the cylinder.

The contact charging fixture 1900 described with reference to FIGS.19-23 is configured to form all the electrets 402 on the cylindricalsurface at once. However, in an alternative embodiment, some of theelectrodes 1906-1910 are omitted, so as to form a subset of theelectrets 402 in a single step. The pressure from the contact chargingfixture 1900 may be released, the fixture 1900 may be rotated, relativeto the cylinder, and then another set of electrets may be formed.

In some circumstances, such as when the electrets 402 are particularlysmall, it may be advantageous to form the electrets 402 in pairs orother small groups, relative to the total number of electrets 402,rather than all at once. Another contact charging fixture, an embodimentof which is shown in FIGS. 29 and 30, enables forming groups ofelectrets on a cylindrical surface, without forming all of the ultimateelectrets at once. This embodiment facilitates repeating the process offorming groups of electrets on successive locations on the cylindricalsurface, including rotating the cylinder between forming each group ofthe electrets.

FIG. 29 is an isometric diagram illustrating a contact charging fixture2900 disposed above a dielectric cylinder 2902 in preparation forforming a pair of electrets, and FIG. 30 is an isometric diagramillustrating the contact charging fixture 2900 in intimate physicalcontact with the dielectric cylinder 2902 workpiece. The contactcharging fixture 2900 includes two electrodes 2904 and 2906,respectively, and an electrically insulative member 2908 separating thetwo electrodes 2904 and 2906. The two electrodes 2904 and 2906 and theelectrically insulative member 2908 between the two electrodes 2904 and2906 collectively form an electrode assembly 2910. End surfaces 2912 and2914 of the electrodes 2904 and 2906 that contact the dielectriccylinder 2902 should form cylindrical sectors. The dielectriccylindrical workpiece 2902 has a longitudinal axis 2916. Each electrode2904 and 2906 has a respective longitudinal axis 2918 and 2920. Thelongitudinal axes 2918, 2920 of the two electrodes 2904 and 2906 and thelongitudinal axis 2916 of the workpiece 2902 are all parallel to eachother.

The electrode assembly 2910 is translatable between two positions,represented by FIGS. 29 and 30, respectively. The electrode assembly2910 is translatable along an axis 2922 that is perpendicular to thelongitudinal axis 2916 of the workpiece 2902. In use, the two electrodes2904 and 2906 are electrically coupled to an electrical power supply3000 (FIG. 30), and the electrode assembly 2910, specifically theelectrodes 2904 and 2906, is brought into intimate physical contact withthe surface of the dielectric cylinder 2902, as shown in FIG. 30,creating an electric field 3002 within the dielectric cylinder 2902 andthereby forming two electrets on a surface of the workpiece 2902.Pressure should be applied by the contact charging fixture 2900,specifically the electrodes 2904 and 2906, on the surface of thedielectric cylinder 2902.

Once the electrets are formed, the electrical power supply 3000 may bedisconnected and the electrode assembly 2910 is withdrawn from thesurface of the dielectric cylinder 2902, as shown in FIG. 29. Then, thedielectric cylinder 2902, or the contact charging fixture 2900, isrotated, for example as indicated by an arrow 3004, a distance to indexthe contact charging fixture 2900, relative to the dielectric cylinder2902, to a position of the next set of electrets. The forming process isrepeated for each subsequent set of electrets.

Although the electrode assembly 2910 is shown with two electrodes 2904and 2906, the electrode assembly 2910 may include any number ofelectrodes. Thus, although described as forming two electrets at a time,the contact charging fixture 2900 may form any number of electrets at atime. As with the contact charging fixture 1900 (FIG. 19), with suitablemodifications, the contact charging fixture 2900 may be configured toform electrets on an inside surface of a cylinder.

Another embodiment of the present invention is a method forcorona-charging defined regions in an electret cylinder. Corona chargingof flat electrets is known. However, as noted, charging curved electretsposes problems for conventional charging methods. FIG. 24 is anisometric diagram of a mask 2400 with an aperture 2402, through whichions may be guided to corona-charge a region defined by the aperture2402 in an electret cylinder or other curved surface. FIG. 25 is anisometric/schematic diagram of the mask 2400, without the electretcylinder, but with other components of a corona charging system,according to an embodiment of the present invention. These componentsinclude an electrode 2500, a conductive mesh 2502, and an array of oneor more sharp, electrically conductive needles 2504 (a “needle array”).

The wall of an electret cylinder (not shown for clarity) is positionedbetween the electrode 2500 and the aperture 2402. A first voltage source2506 is connected to the needle array 2504, causing air to ionize nearthe needle points. The potential between the electrode 2500, which hasopposite polarity to the needles 2504, accelerates ions through theaperture 2402 and onto the electret cylinder. The mask 2400 preventsions from reaching areas of the electret cylinder, other than a regionexposed through the aperture 2402. The mesh grid 2502 is connected to asecond voltage source 2508 with the same polarity as the first voltagesource 2506 used to charge the needles 2504, but of a lower amplitude.The mesh grid 2502 promotes uniform distribution of charge on theelectret cylinder.

The charged region on the electret is given a positive or negativecharge, depending on the polarity of voltage sources 2506 and 2508,respectively. Reversing the polarity of both voltage sources 2506 and2508, or exchanging the relative positions of (a) the needle array 2504and mesh grid 2502 and (b) the electrode 2500, causes an electret regionto be charged to the opposite polarity. Alternating regions of positiveand negative charge may be created on the electret cylinder by: (1)charging a region of the electret cylinder with a first charge, then (2)rotating the electret cylinder, relative to the mask, so the aperture2402 reveals an uncharged region of the electret cylinder, then (3)corona charging the uncharged region with a charge opposite the firstcharge and repeating the process for the remaining desired regions. Theneedle array 2504, the mesh grid 2502, the mask 2400 and the electrode2500 are maintained in a fixture orientation, relative to one another.

In an alternative embodiment for corona charging, multiple regions onthe electret cylinder may be simultaneously charged. In this embodiment,the mask 2400 contains multiple apertures 2402, and the electrode 2500forms a complete cylinder, or at least has portions disposed under eachaperture 2402. A separate needle array 2504 is positioned above eachaperture 2402. All the needle arrays 2504 are made electrically commonto the needle array voltage source 2506. The mesh grid 2502 forms acomplete cylinder, enclosing the mask 2400, or at least has portionsdisposed between each needle array 2504 and its corresponding aperture2402. Activating the voltage sources causes a pattern of polarizedregions to be created on the electret cylinder. An equal number ofpolarized regions of the opposite polarity may be created by: (1)charging a plurality of regions of the electret cylinder, then (2)disconnecting the voltage sources, (3) rotating the electret cylinder,relative to the mask, such that the apertures 2402 align withun-polarized regions of electret material, and then (4) reconnecting thevoltage sources 2506 and 2508, but with reversed polarity.

In another embodiment, two sets of voltage sources, needle arrays, meshgrids and electrodes are used, with each set configured to charge theelectret cylinder with an opposite charge. In this embodiment, the maskdefines an aperture for each region of the electret cylinder that is tobe charged. This embodiment does not require rotating the electretcylinder. Both polarities of regions on the electret cylinder may becharged simultaneously, or each polarity may be charged in turn.

Contact charging, liquid contact charging and corona charging aredescribed in Kao, Kwan Chi, “Dielectric Phenomena in Solids,” ISBN9780123965625, Academic press, 2504.

Imbedded Electrets

Rather than form the electrets in the cylinder of electret material 400,the electrets may be formed as separate strips or other suitable shapesand attached to the cylinder. The electrets may be attached to thesurface of the cylinder, such as by a suitable adhesive. Alternatively,the electrets may be press fit or interference fit into suitable groovesin the surface of the cylinder. Optionally, the electrets may have across-sectional shape, such as a trapezoid, that locks into a similarcross-sectional shape defined by the groove, when the electret ispressed into the groove.

Hydrostatic or Aerostatic Bearing

FIG. 31 is an isometric diagram of a hydrostatic or aerostatic(depending on whether the dielectric fluid 1004 is a liquid or a gas)bearing 3100 between a rotor 1000 and a stator 1002 of an electrostaticmotor. For simplicity of explanation, the term hydrostatic, as usedherein, including in the claims, means hydrostatic or aerostatic. Thehydrostatic bearing 3100 defines a plurality of ports, represented byports 3102, 3104 and 3106, extending through respective electrodes 402.FIG. 32 is a cross-sectional view of a portion of the rotor 1000 andstator 1002 showing one fluid port 3102 of the hydrostatic bearing 3100extending through one of the electrodes 306. Dielectric fluid flows, asindicated by an arrow 3200, as a result of rotation 3202 of the rotor1000 into the cylindrical shell defined between the rotor 1000 and thestator 1002. The dielectric fluid flow supports the rotor 1000 withinthe stator 1002.

While the invention is described through the above-described exemplaryembodiments, modifications to, and variations of, the illustratedembodiments may be made without departing from the inventive conceptsdisclosed herein. For example, although specific parameter values, suchas dimensions and materials, may be recited in relation to disclosedembodiments, within the scope of the invention, the values of allparameters may vary over wide ranges to suit different applications.Unless otherwise indicated in context, or would be understood by one ofordinary skill in the art, terms such as “about” mean within ±25%.

As used herein, including in the claims, the term “and/or,” used inconnection with a list of items, means one or more of the items in thelist, i.e., at least one of the items in the list, but not necessarilyall the items in the list. As used herein, including in the claims, theterm “or,” used in connection with a list of items, means one or more ofthe items in the list, i.e., at least one of the items in the list, butnot necessarily all the items in the list. “Or” does not mean “exclusiveor.”

Disclosed aspects, or portions thereof, may be combined in ways notlisted above and/or not explicitly claimed. In addition, embodimentsdisclosed herein may be suitably practiced, absent any element that isnot specifically disclosed herein. Accordingly, the invention should notbe viewed as being limited to the disclosed embodiments.

What is claimed is:
 1. An electrostatic motor, comprising: a rotor,rotatable about a rotation axis and defining a first cylindrical surfacehaving a longitudinal axis coincident with the rotation axis and havinga first plurality of elongated charge members disposed circumferentiallyon the first cylindrical surface, each first charge member extendingparallel to the longitudinal axis; a stator defining a secondcylindrical surface counterfacing, and spaced apart from, the firstcylindrical surface and having a second plurality of elongated chargemembers disposed circumferentially on the second cylindrical surface,each second charge member extending parallel to the longitudinal axis;wherein the first plurality of charge members is configured to havealternating polarities along the circumference of the first cylindricalsurface and the second plurality of charge members is configured to havealternating polarities along the circumference of the second cylindricalsurface; wherein one surface of the first and second cylindricalsurfaces is an outside cylindrical surface, and the other surface of thefirst and second cylindrical surfaces is an inside cylindrical surface,the first and second surfaces defining a cylindrical shell therebetween;and a dielectric filling the cylindrical shell.
 2. An electrostaticmotor according to claim 1, wherein the dielectric comprises adielectric fluid.
 3. An electrostatic motor according to claim 2,wherein the dielectric fluid is pressurized to greater than about 101kPa absolute pressure.
 4. An electrostatic motor according to claim 2,further comprising means for pressurizing the dielectric fluid togreater than about 101 kPa absolute pressure.
 5. An electrostatic motoraccording to claim 2, further comprising: a filter in fluidcommunication with the cylindrical shell; and a pump configured tocirculate the dielectric fluid from the cylindrical shell, through thefilter and then back to the cylindrical shell.
 6. An electrostatic motoraccording to claim 2, wherein at least one surface of the first andsecond cylindrical surfaces defines a plurality of features that extendproud of the at least one surface.
 7. An electrostatic motor accordingto claim 6, wherein each feature of the plurality of features comprisesa chevron shape.
 8. An electrostatic motor according to claim 1, whereinthe dielectric comprises a partial vacuum.
 9. An electrostatic motoraccording to claim 1, wherein: one plurality of charge members of thefirst and second pluralities of charge members comprises a plurality ofelectrets arranged such that adjacent electrets are of opposite charge;and the other plurality of charge members of the first and secondpluralities of charge members comprises a first plurality of electrodes.10. An electrostatic motor according to claim 9, wherein charges onadjacent electrets of the plurality of electrets are sufficient toexceed breakdown voltage of air over a distance equal to spacing betweenthe adjacent electrets.
 11. An electrostatic motor according to claim 9,wherein the one plurality of charge members further comprises a secondplurality of electrodes.
 12. An electrostatic motor according to claim9, further comprising a plurality of charging electrodes, one chargingelectrode of the plurality of charging electrodes for each respectiveelectret of the plurality of electrets, each charging electrode beingdisposed below, and in intimate contact with, the respective electret.13. An electrostatic motor according to claim 1, wherein: one pluralityof charge members of the first and second pluralities of charge memberscomprises a first plurality of electrodes; and the other plurality ofcharge members of the first and second pluralities of charge memberscomprises a second plurality of electrodes.
 14. An electrostatic motoraccording to claim 1, further comprising an electronic circuitconfigured to energize and commutate one plurality of charge members ofthe first and second pluralities of charge members.
 15. An electrostaticmotor according to claim 1, further comprising a hydrostatic bearingconfigured to support the rotor within the stator, the hydrostaticbearing defining a plurality of fluid ports extending from an outersurface of the stator to an inner surface of the stator, ones of theplurality of fluid ports extending through ones of the second pluralityof charge members, one end of each fluid port of the plurality of fluidports being in fluid communication with the cylindrical shell.
 16. Anelectrostatic motor according to claim 2, wherein at least one surfaceof the first and second cylindrical surfaces defines a plurality offeatures.
 17. An electrostatic motor, comprising: a rotor, rotatableabout a rotation axis and defining a first cylindrical surface having alongitudinal axis coincident with the rotation axis and having a firstplurality of elongated charge members disposed circumferentially on thefirst cylindrical surface, each first charge member extending parallelto the longitudinal axis; a stator defining a second cylindrical surfacecounterfacing, and spaced apart from, the first cylindrical surface andhaving a second plurality of elongated charge members disposedcircumferentially on the second cylindrical surface, each second chargemember extending parallel to the longitudinal axis; wherein at least oneof the first and second pluralities of charge members comprises aplurality of electrets; wherein one surface of the first and secondcylindrical surfaces is an outside cylindrical surface, and the othersurface of the first and second cylindrical surfaces is an insidecylindrical surface, the first and second surfaces defining acylindrical shell therebetween; and a dielectric filling the cylindricalshell.
 18. An electrostatic motor, comprising: a rotor, rotatable abouta rotation axis and defining a plurality of first cylindrical surfaces,each first cylindrical surface having a respective longitudinal axiscoincident with the rotation axis, each first cylindrical surface havinga first plurality of elongated charge members disposed circumferentiallythereon, each charge member of the first plurality of elongated chargemembers extending parallel to the longitudinal axis; a stator defining aplurality of second cylindrical surfaces, each second cylindricalsurface counterfacing, and spaced apart from, a corresponding one of thefirst cylindrical surfaces, each second cylindrical surface having asecond plurality of elongated charge members disposed circumferentiallythereon, each charge member of the second plurality of elongated chargemembers extending parallel to the longitudinal axis; wherein one surfaceof each of the pluralities of the first and corresponding secondcylindrical surfaces is an outside cylindrical surface, and the othersurface of each of the pluralities of the first and corresponding secondcylindrical surfaces is an inside cylindrical surface, each firstsurface and corresponding second surface defining a cylindrical shelltherebetween; and a dielectric filling each cylindrical shell.
 19. Anelectrostatic motor according to claim 18, wherein the dielectriccomprises a dielectric fluid.
 20. An electrostatic motor according toclaim 19, wherein the dielectric fluid is pressurized to greater thanabout 101 kPa absolute pressure.
 21. An electrostatic motor according toclaim 19, further comprising means for pressurizing the dielectric fluidto greater than about 101 kPa absolute pressure.
 22. An electrostaticmotor according to claim 19, further comprising: a filter in fluidcommunication with the cylindrical shell; and a pump configured tocirculate the dielectric fluid from the cylindrical shell, through thefilter and then back to the cylindrical shell.
 23. An electrostaticmotor according to claim 18, wherein at least one surface of thepluralities of first and second cylindrical surfaces defines a pluralityof features.
 24. An electrostatic motor according to claim 23, whereineach feature of the plurality of features comprises a chevron shape. 25.An electrostatic motor according to claim 18, wherein the dielectriccomprises a partial vacuum.
 26. An electrostatic motor according toclaim 18, wherein for one of the first cylindrical surfaces and acorresponding one of the second cylindrical surfaces: one plurality ofcharge members of the first and second pluralities of charge memberscomprises a plurality of electrets arranged such that adjacent electretsare of opposite charge; and the other pluralities of charge members ofthe first and second pluralities of charge members comprises a firstplurality of electrodes.
 27. An electrostatic motor according to claim26, wherein charges on adjacent electrets of the plurality of electretsare sufficient to exceed breakdown voltage of air over a distance equalto spacing between the adjacent electrets.
 28. An electrostatic motoraccording to claim 26, wherein the one plurality of charge membersfurther comprises a second plurality of electrodes.
 29. An electrostaticmotor according to claim 26, further comprising a plurality of chargingelectrodes, one charging electrode of the plurality of chargingelectrodes for each respective electret of the plurality of electrets,each charging electrode being disposed below, and in intimate contactwith, the respective electret.
 30. An electrostatic motor according toclaim 18, wherein for one of the first cylindrical surfaces andcorresponding one of the second cylindrical surfaces: one plurality ofcharge members of the first and second pluralities of charge memberscomprises a first plurality of electrodes; and the other plurality ofcharge members of the first and second pluralities of charge memberscomprises a second plurality of electrodes.
 31. An electrostatic motoraccording to claim 18, further comprising an electronic circuitconfigured to energize and commutate one plurality of charge members ofthe first and second pluralities of charge members.
 32. An electrostaticmotor according to claim 18, further comprising a hydrostatic bearingconfigured to support the rotor within the stator, the hydrostaticbearing defining a plurality of fluid ports extending from an outersurface of the stator to an inner surface of the stator, ones of theplurality of fluid ports extending through ones of the second pluralityof charge members, one end of each fluid port of the plurality of fluidports being in fluid communication with the cylindrical shell.
 33. Anelectrostatic motor according to claim 18, wherein the plurality offirst cylindrical surface is attached via at least one first disk ashaft for rotation therewith, the shaft extending collinear with theaxis of rotation, and wherein the plurality of second cylindricalsurfaces is attached together via at least one second disk, relative towhich the first disk is configured to rotate.